The prevention of lowered contrast and lowered visibility caused by external light reflection or image reflection is required of image display devices, for example, cathode-ray tube display devices (CRTs), plasma displays (PDPs), organic or inorganic electroluminescent displays (ELDs), field emission displays (FEDs), or liquid crystal displays (LCDs). Accordingly, it is common practice to provide an antireflection laminate on the outermost surface of an image display device from the viewpoint of reducing image reflection or reflectance using the principle of light scattering or the principle of optical interference.
In image display devices, for example, liquid crystal displays, the use of an anti-dazzling laminate as one of antireflection laminates has hitherto been known for regulating optical properties to realize excellent image displays. The anti-dazzling laminate is utilized for preventing a lowering in visibility as a result of external light reflection or image reflection within image display devices. The anti-dazzling laminate is generally realized by forming an anti-dazzling layer having a concavoconvex shape on a base material. In image display devices, for example, liquid crystal displays, the use of an anti-dazzling laminate as one of antireflection laminates has hitherto been known from the viewpoint of regulating optical properties to realize excellent image display. The anti-dazzling laminate is utilized for preventing a lowering in visibility as a result of external light reflection or image reflection within image display devices.
In recent years, a demand for a higher level of definition of panel resolution has led to a higher level of fineness of the concavoconvex shape of the anti-dazzling layer. Accordingly, a concavoconvex shape having a broad and large curve has been regarded as unsuitable for meeting a demand for higher definition in the anti-dazzling laminate having the above construction and thus have not been adopted. On the other hand, when increasing the fineness of the concavoconvex shape involved in higher definition of panel resolution can meet a demand for higher definition of the panel resolution. Regarding this technique, however, it has often been pointed out that external light is reflected from the display surface resulting in such a phenomenon that, for example, the image display surface is seen white (whitening), or lowered contrast. When the anti-dazzling laminate having the concavoconvex shape is used on the image display surface of notebook computers and the like, a certain level of satisfactory optical properties can be provided. When the light transmitted through the backside of backlight within a display is transmitted through the concavoconvex shape face of the anti-dazzling laminate formed on the outermost surface of the panel, however, the concavoconvex shape functions as fine lenses which disturb the displayed pixels and the like, that is, “glare” is likely to occur. This unfavorable phenomenon makes it difficult to satisfactorily attain the effect of the anti-dazzling laminate per se.
In order to eliminate this “glare” involved in an enhancement in panel resolution, for example, a method has been adopted in which surface concavoconvexes are densely provided to enhance the sharpness and, at the same time, scattering particles different from the resin for anti-dazzling layer formation in refractive index are added to, for example, impart internal scattering effect to the anti-dazzling laminate. All of proposed methods could satisfactorily solve the problem of the “glare,” but on the other hand, they sometimes lowered the visibility of the whole image. On the other hand, in the anti-dazzling laminate, the method for preventing the “glare” in high-definition panels has been regarded as a main cause of an unfavorable phenomenon, for example, a deterioration in contrast such as clouding (opacification) caused by surface whitening or internal scattering effect. That is, it has been regarded that “glare prevention” and “contrast improvement” are in the relationship of tradeoff, and simultaneously meeting both the requirements is difficult. In the above methods, for example, black color reproduction in on-screen display has sometimes been poor. That is, gradation rendering of black color in a light room, particularly a black color gradation difference in low gradation, cannot be regarded without difficulties resulting in lowered sensitivity. Specifically, black and gray colors are only recognized as a blurred and identical color-tone black color. In particular, an anti-dazzling laminate having better anti-glare properties has a significantly lowered level of visibility.
On the other hand, a light diffusion layer having light diffusion properties improved by bringing the ratio between the internal haze and the whole haze to 2 to 1000 and bringing the internal haze to not less than 5% has been proposed (Japanese Patent Laid-Open No. 295729/1999). Further, an anti-dazzling laminate has been proposed in which glare preventive effect and white blurring preventive effect can be effectively attained by bringing the whole haze value to not less than 35% and not more than 50%, bringing the internal haze value to not less than 20% and not more than 40%, and bringing the internal haze value/whole haze value to not less than 0.5 and not more than 0.8 (U.S. Pat. No. 3,703,133). According to studies by the present inventors, however, any anti-dazzling laminate, which can realize contrast high enough to realize satisfactory reproduction of black of images (black color reproduction) in a light room and can prevent glare feeling, has not been developed yet.
Accordingly, at the present time, the development of an optical laminate, which can realize good anti-dazzling properties and black color reproduction and, at the same time, can effectively prevent the glare of an image surface, has been desired. In particular, an optical laminate, which can be used in liquid crystal displays (LCDs) as well as in other applications such as cathode-ray tube display devices (CRTs), plasma displays (PDPs), fluorescent display tubes, and field emission displays, has been eagerly desired.